This invention relates to the protection of electrical loads from damage caused by phase line failure in a polyphase power supply to which the load is connected.
Polyphase power system failure detectors for protecting electrical loads, are of course well known. Such power failure detectors often sense one or more failure conditions including phase unbalance, reduction in voltage level and often require a predetermined sequence of connections to the power phase lines for proper operation. Sometimes, such power failure detectors are limited to a predetermined power cycle frequency. In responding to voltage drop or current unbalance as the sensed conditions of power failure, prior power failure detectors are sometimes triggered into operation unintentionally as a result of momentary or transient conditions of little concern.
It is therefore an important object of the present invention to provide a power failure detector which is less likely to unintentionally respond to transient conditions and which is more versatile in use for protecting equipment powered at different voltage levels and different cycle frequencies.